1. Field of the Invention
The present invention relates to filters and filter media. More particularly, the present invention relates to a composite filter media for filtering contaminants from a fluid and fluid filters containing the composite filter medium.
2. Description of the Prior Art
Fluids, such as liquids or gases, typically contain contaminants which include particulates, chemicals, and organisms. In many cases, it is desirable to remove some or all of such contaminants from the fluid. Usually, contaminants are removed from a fluid supply by passing the fluid through a filter whereby the contaminants are separated from the filtered fluid or filtrate.
Water is probably the most highly filtered fluid as it is filtered in industrial processes as well as in the household. Purification of water to produce potable water often requires the simultaneous reduction of particulate contaminants, dissolved organic chemicals and inorganic heavy metals. Particulate contaminants may include dirt, rust, silt, and other particles as well as potentially hazardous microorganisms such as chlorine resistant protozoan cysts, such as Cryptosporidium Parvum or Giardia, or bacteria such as Cholera and E. coli. Organic chemicals may include those that contribute to taste and odor as well as potentially toxic pesticides, chlorinated hydrocarbons, and other synthetic organic chemicals. Free chlorine reduction is also a major objective when the residual concentration of this disinfectant is sufficiently high to cause a bad taste. The most common heavy metal found in domestic water is lead derived from brass fixtures, leaded solder, lead pipes or other sources. Other heavy metals often found in drinking water include copper, zinc, manganese and iron.
The most common household water filters are typically small trapezoidal shaped plastic containers filled with a loose adsorbent medium such as activated carbon, ion exchange resins or zeolites. Water is filtered by such water filters by passing it through the loose adsorbent medium in an axial direction from a wider to a narrower portion of the trapezoidal container.
The trapezoidal shaped filter element is often used in a carafe and when used in a carafe is typically called a gravity-flow carafe filter. Such filters are typically installed within a household carafe having an upper reservoir, a lower reservoir and a filter receptacle fitted at the bottom of the upper reservoir. The trapezoidal shaped filter element is installed in the carafe by wedging it into the receptacle so as to effect a seal between the two reservoirs. Water passing from the upper reservoir to the lower reservoir must pass through the filter element. Typically, water enters the filter element through a series of small perforations at the wider top of the trapezoid. The water flows through the filter to the narrower bottom while traversing the porous bed of loose adsorbent. The water passes through a series of micro perforations in the narrower bottom of the filter exiting into the lower reservoir. In some filters, one or more non-woven pads, functioning as a fines filter, may be installed at the bottom, top or both bottom and top of the filter element to prevent the release of fine particles from the adsorbent bed.
The flow rate through present day gravity-flow carafe filters as described above is generally slow, typically about 200 ml per minute for a filter loaded with 100 grams of mixed wet resin-carbon filter medium containing water in an amount of about 30 to 35 percent by weight. The slow flow rate occurs because: (1) the water must traverse a deep bed of adsorbent particles; (2) the filter operates in a low pressure environmentxe2x80x94only the pressure of the overlying water in the upper reservoir, typically several inches of water, is available to force the water through the filter; and (3) the size of the adsorbent particles are limited. Excessively large particles that would permit faster flow rates, would also have slower adsorption kinetics. This forces the use of relatively small particles (about 35 mesh) having faster adsorption kinetics but greater flow restriction. In view of the above constraints, a liter of water normally takes about 5 to 10 minutes or more to process through the present day carafe filter.
It is desirable to have a high flow rate, gravity-flow carafe filter which is capable of intercepting the very small chlorine resistant cysts such as Giardia and Cryptosporidium Parvum. It is also desirable to provide a high flow rate, gravity-flow carafe filter with enhanced chlorine, taste and odor reduction as well as a filter that can absorb heavy metals such as lead. It is desirable to provide a high flow filter that supports high flow with a 1 inch water column and that intercepts 99.95 percent of 3 to 4 micron particles which makes it suitable for cyst reduction and which generally meets NSF Class 1 particle reduction requirements. Mass production of carafe filters with simple equipment and at low cost is a necessity.
It is a primary object of the present invention to provide a fluid filter that is capable of filtering contaminants from a fluid at relatively high flow rates while providing a relatively low resistance to fluid flow.
It is another object of the present invention to provide a fluid filter capable of filtering chlorine resistant cysts such as Giardia and Cryptosporidium Parvum. 
It is yet another object of the present invention to provide a high flow rate carafe filter with enhanced chlorine, taste and odor reduction as well as a filter that can absorb heavy metals such as lead.
It is still another object of the present invention to provide a carafe filter that can be mass produced with simple equipment and at low cost.
In accordance with the objects of the present invention, the foregoing primary objective is realized by providing a low flow resistance composite filter medium for removing at least 99.95 percent of particulates of a size in the 3 to 4 micron range and dissolved chemical contaminants from a fluid comprising an adsorbent layer containing an adsorbent agent and a hydrophilic particulate intercepting layer disposed adjacent to the adsorbent layer. The composite medium has a mean flow pore diameter of about 1 to 10 microns, a bubble point of about 3 to 15 microns and an air permeability of about 0.5 to 7 liters per minute/cm2 with a pressure drop of about 0.1 bar.
Other objects and advantages of the invention will be apparent from the following detailed description and the accompanying drawings.